Diacylglycerol kinase theta is translocated and phosphoinositide 3-kinase-dependently activated by noradrenaline but not angiotensin II in intact small arteries.

Diacylglycerol (DG) kinase (DGK) phosphorylates the lipid second messenger DG to phosphatidic acid. We reported previously that noradrenaline (NA), but not angiotensin II (AII), increases membrane-associated DGK activity in rat small arteries [Ohanian and Heagerty (1994) Biochem. J. 300, 51-56]. Here, we have identified this DGK activity as DGKtheta, present in both smooth muscle and endothelial cells of these small vessels. Subcellular fractionation of artery homogenates revealed that DGKtheta was present in nuclear, plasma membrane (and/or Golgi) and cytosolic fractions. Upon NA stimulation, DGKtheta translocated towards the membrane and cytosol (155 and 153% increases relative to the control, respectively) at 30 s, followed by a return to near-basal levels at 5 min; AII was without effect. Translocation to the membrane was to both Triton-soluble and -insoluble fractions. NA, but not AII, transiently increased DGKtheta activity in immunoprecipitates (126% at 60 s). Membrane translocation and DGKtheta activation were regulated differently: NA-induced DGKtheta activation, but not translocation, was dependent on transient activation of phosphoinositide 3-kinase (PI 3-K). In addition, DGK activity co-immunoprecipitated with protein kinase B, a downstream effector of PI 3-K, and was increased greatly by NA stimulation. The rapid and agonist-specific activation of DGKtheta suggests that this pathway may have a physiological role in vascular smooth-muscle responses.